Study On Introduced Cultivars Of Green Jujube (Zizyphus Mauritiana Lamk) In Horticultural Greenhouse

Introduced cultivars of green jujube (Zizyphus mauritianaAaink) were cultivated in greenhouses at Chaoyang, north China's Liaoning Province and Changping, Beijing. Contrast trials about biological and photosynthetic characteristics, leaf nutrition and biological properties of pollen were carried out. Relevant planting, training, pruning and propagation methods were studied. The cultivars suitable to be cultivated in greenhouses in Northern China were selected. The corresponding agronomic techniques and propagation methods were established. The results show as follows:(1) The introduction of some cultivars of green jujube proved successful in greenhouses concerning such aspects as tree growth, flowering and fruiting, no severe plant diseases or insect pests were observed, and their native characteristics could be maintained well. Therefore, they could be cultivated as new resources of fruit trees in Northern China. Besides, the simple and easy agronomic techniques of green jujube make it suitable for its popularization among farmers in Northern China.(2) The comprehensive evaluation showed that cultivars like "Galo", "Wuqianzhong", "Dashijie", "Cuimi" and "Mizao" were suitable to be cultivated in greenhouses in Northern China; "Huangguan" and "Biyun", however, were not suitable; "Fuzao", "Roulong" and "Miandian" need further trials.(3) The agronomic techniques of green jujube were very important in greenhouses when they were cultivated in Northern China. The coppice management could help trees grow normally in greenhouses and improve the yield and quality of fruits. The coppice management should be carried out from late March to April with an optimum height of 30 cm. Pruning could adjust the trees' shape and accelerate their growth and fruiting rate. The peak buds should be cut down when the branches reach 80 cm long. The element Mg is in great need during the growth of green jujube, and 0.5% MgSO₄ solution should be sprayed from September to November when the trees were in their florescence. A spray with 15 mg/L GA and ringing in florescence stage could obviously accelerate the fruiting amount.(4) The medium containing 1% agar, 15% sucrose and 0.02% BA with a temperatureof 30—32 °C is the optimum condition for the test of pollen germination rate. The cultivars of "Dashijie", "Cuimi", "Roulong", "Miandian" and "Gaolang" were better in pollen fertility considering the indexes like pollen germination rate, pollen abnormality rate and pollen amount.(5) The most suitable propagation method was grafting, and a cion with two or three buds of the desired cultivars is the best choice. Seedlings of wild species of ber were used as rootstocks, which were sown by stones. The stones must be soaked in water for at least 60 hours before sown. The best season in North China for successful propagation by wedge grafting is July or August. Grafting with a cion over one year old on a stock with a stem diameter of at least 0.6-0.8 cm could get a survival rate of over 90%.(6) The fruits of green jujube have many nice characteristics, and its pollen has a higher germination rate, better fertility and longer preservation time than many other native Chinese jujube cultivars. Therefore, several cultivars of green jujube could be used as parents to crossbreed with other Chinese jujube cultivars.